This invention relates to a device for measuring temperature, particularly the temperature of an animal or human body.
Sensors for measuring temperature are well known and include thermistors, thermocouples and semiconductor-based electronic sensors. If correctly calibrated, such sensors can provide an indication of the temperature of an object in the region from which the sensor takes its inputs. For example, a thermistor placed in direct contact with an object will give an indication of the temperature of that part of the object with which the sensor is in contact.
Often, an object does not have a uniform temperature and its measured temperature varies throughout its volume. For example, the temperature of an animal or human typically varies from its core body temperature to skin temperature. Skin temperature can vary considerably with environmental conditions and it is therefore the core body temperature which is typically more important for medical and diagnostic applications. However, it is not always possible or convenient to measure core body temperature directly by invasive means. It is preferable to make one or more measurements of an easily accessible part of the body (such as skin temperature) and estimate core body temperature from those measurements.
US Patent Application No. 2007/0282218 discloses a device for measuring the local temperature of an external surface of a body using at least two temperature sensors separated by an insulating layer. The measurements may be used to calculate core body temperature by correcting for a difference between core body temperature and local temperature. Algorithms for performing such a correction in dependence on known thermal characteristics of the body are well known in the art (for example, see “Computation of mean body temperature from rectal and skin temperatures”, Journal Applied Physiology 31: 484-489, 1971).
An example of a conventional device 12 for measuring the temperature of a body 11 is shown in FIG. 1. Temperature sensors 13 and 14 are arranged at different distances from the external surface 18 of body 11 in material 15, and are separated by a thermally-insulating barrier 16. The effect of thermally-insulating barrier 16 is to cause temperature sensors 13 and 14 to attain different equilibrium temperatures at different rates, such that a measurement of the temperature of body 11 can be estimated from the heat flow across the device between the first and second sensors.
Conventional devices measure the heat flow from the subject body into the device and require that the temperature sensors are accurately positioned so as to properly capture the flow of heat across the device. The accuracy of such devices is therefore heavily dependent on the accuracy of placement of the sensors of the device. Furthermore, the devices are readily influenced by other sources of heat in their environment.
There is therefore a need for a device for measuring temperature whose accuracy is less dependent on the accuracy of placement of its temperature sensors and the proximity of other sources of heat in its environment.